1. Field of the Invention
The invention relates to a mercury lamp of the short arc type. The invention relates especially to a mercury lamp of the short arc type which is used for a semiconductor exposure device.
2. Description of the Related Art
In the exposure process in the manufacture of semiconductors, recently a mercury lamp of the short arc type has been used which emits UV radiation with a main wavelength of 365 nm (hereinafter called the "i-line"). Since the degree of integration of an integrated solid-state circuit increases each year, accordingly, there is a greater and greater demand for image resolution during exposure. Furthermore, due to the increase in the exposure surface as a result of increasing the wafer aperture or due to the modified illumination which is used to achieve high image resolution, there is a demand for an increase in the amount of UW radiation from the light source (which is hereinafter called only the "amount of radiation").
Furthermore, there is also a demand for an increase in the throughput as an indicator of the amount of production per unit of time. Therefore, for the lamp as a light source there is a demand for high radiation efficiency, and for an emission device which comprises this light source, there is a demand for high focusing efficiency.
To obtain intensive i-line radiation, conventionally, a process was used in which the input power supplied to the lamp is increased. However, when the input power supplied to the lamp is increased, the thermal burden on the electrodes increases, causing more vigorous vaporization of the electrode material and acceleration of blackening of the arc tube. Furthermore, by increasing the input power, the arc tube necessarily has a larger outside dimension, by which a larger air blower device is needed to dissipate the heat produced by the lamp. A process in which the input power supplied to the lamp is increased to obtain intensive i-line radiation is therefore not desirable.